Remove erroneous limitation on max number of args for --plugin

Remove erroneous limitation on max number of args for --plugin

Commit 3d6a4cded2 introduced a maximum limit of possible arguments
for most options, to error out on config lines with too-many args.

Commit 82acf21634 extended the limit for "--plugin" to accept "one
mandatory, one optional" argument.

Both are wrong - "--plugin" can accept an arbitrary number of arguments,
but this is not directly obvious from options.c, one needs to check
plugins.c / plugin_option_list_add() and misc.c / make_extended_arg_array()
to see that.

Thus, remove the max limit for "--plugin" completely.

(Reported by SviMik on IRC)

Signed-off-by: Gert Doering <gert@greenie.muc.de>
Acked-by: Steffan Karger <steffan.karger@fox-it.com>
Message-Id: <20170518191311.4769-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg14678.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>